Prime lens

The invention discloses a prime lens which comprises two lens groups separated by an aperture, the lens group close to the magnification side comprises three lenses, the lens group close to the reduction side comprises five lenses, and during focusing, the distance among the first lens group, the aperture and the second lens group is fixed and moves along an optical axis relative to a light valve. The first lens group and the second lens group are respectively provided with an aspheric lens. And the total length of the optical path of the prime lens is less than or equal to 150mm. 本发明揭露了一种定焦镜头，包括被光圈分隔的两个透镜群，靠近放大侧的透镜群包括三枚透镜，靠近缩小侧的透镜群具有五枚透镜，在对焦时，第一透镜群、光圈及第二透镜群之间的距离为固定且一并相对于光阀沿光轴移动。第一透镜群及第二透镜群分别具有一非球面透镜。定焦镜头的光程总长小于等于150mm。